Premium
Excess Nitrate Export in Mountaintop Removal Coal Mining Watersheds
Author(s) -
Brooks Alexander C.,
Ross Matthew R. V.,
Nippgen Fabian,
McGlynn Brian L.,
Bernhardt Emily S.
Publication year - 2019
Publication title -
journal of geophysical research: biogeosciences
Language(s) - English
Resource type - Journals
eISSN - 2169-8961
pISSN - 2169-8953
DOI - 10.1029/2019jg005174
Subject(s) - watershed , ecoregion , environmental science , streams , hydrology (agriculture) , land reclamation , coal mining , nitrate , water quality , sampling (signal processing) , coal , geology , geography , ecology , computer network , geotechnical engineering , machine learning , computer science , biology , archaeology , filter (signal processing) , computer vision
Abstract Throughout the Central Appalachian ecoregion, mountaintop removal coal mining (MTM) is the predominant form of land use change. The streams draining MTM impacted watersheds have been reported to contain high stream nitrate (NO 3 − ) concentrations, yet the source and persistence of elevated NO 3 − remains unknown. Here we compiled data from multiple sources to conduct a regional evaluation of the impact of mining on stream NO 3 − , examine NO 3 − persistence after mining cessation, and identify potential N sources. Using water quality data from six large watersheds, we observe elevated NO 3 − in watersheds with the highest active mining density. At four small MTM watersheds with repeat sampling, we found that high levels of NO 3 − concentrations declined after mining cessation but remain elevated above reference after several decades. At MTM watersheds, we found annual mass flux of NO 3 − was 3.68 to 26.4 kg N ha −1 year −1 , which is 1 to 2 orders of magnitude higher than a nearby forested reference watershed. Stream water NO 3 − isotopic ratios at these sites did not match previously suggested NO 3 − sources such as explosives used during mining and fertilizer applied during reclamation but were highly enriched in both δ 15 N and δ 18 O compared to the reference watershed suggesting high rates of NO 3 − retention. Explosive residue could account for the bulk of watershed NO 3 − export during active mining phases but other mining related N sources including fertilizer and rock‐derived N, the construction of valley fills, and alterations in watershed NO 3 ‐ cycling likely contribute to the persistence of elevated NO 3 − export observed in this study.